Heat insulating meatal sheets



United States Patent 4 Claims. or. 156-325) This invention relates to metal sheets having heat insulating properties.

Sheet metal reacts unfavourably to the action of heat or fire owing to its good thermal conductivity. It quickly becomes heated to above red heat and therefore constitutes little hindrance to the spread of a fire.

It is known to provide sheet metal or structural components made of sheet metal with insulating coatings. Upon the prolonged action of heat, however, these coattings become cracked owing to variable thermal expansion, so that their insulation effect is lost.

US. patent application Serial No. 175,823, filed February 26, 1962, by Rudolf Breu, Rudolf Gaeth, Bernhard Schmitt and Horst Nebel, describes fireproofing compositions in the form of sheets or structural components made therefrom which comprise an alkali metal silicate, preferably sodium silicate, which contains Water in an amount of 20 to 70% by weight, preferably 40 to 60% by Weight, and fibers, preferably synthetic silicate fibers, in an amount of to 40% by weight, preferably to 25% by Weight, said percentages being with reference to anhydrous alkali metal silicate. The fibers may be glass fibers, rock wool and the like. The alkali silicate should have a molar ratio of alkali metal oxide to silicon dioxide of about 1:2 to 1:4, preferably of from 1:25 to 1:35. The fibers should have a minimum length of about 30 mm.

It is an object of the present invention to provide metal sheets combined with a heat insulating substance which sheets will not lose their insulating effect even upon prolonged exposure to heat. It is a further object of the present invention to provide a process for the production of such heat insulating metal sheets. These objects are achieved by sheet metal which is combined with alkali metal silicate sheets containing fibers and water.

The composite sheets according to this invention may be prepared simply by combining sheet metal with the fireproofing sheets with a suitable adhesive, for example waterglass solution. Composite sheets of this type may be made particularly advantageously by pressing together the fireproofing sheets and the sheet metal, preferably consisting of iron, in a heated press at temperatures of 50 to 150 C., preferably of 80 to 120 C. The pressure to be maintained during the pressing depends on the temperature used. Coherent composite sheets are obtained at higher temperatures, for example at about 140 C., with lower pressures than when pressing at lower temperatures, for example at 80 C. Thus for example at temperatures of about 140 C. a pressure of about atmospheres is suitable with a pressing time of about five to ten minutes. Even lower pressures are sufficient with longer pressing times. The most favorable pressure and time at a given temperature may be ascertained in dependence on the thickness of the sheet by a simple preliminary experiment. Composite sheets according to the invention may however be produced continuously by passing the sheet metal and the fireproofing sheets between two heated pairs of synchronized rollers under pressure. The composite sheets according to this invention may be provided with a fireproofing sheet of an alkali silicate containing water and fibers on one side or on both sides of the sheet metal. It is also possible ice however to provide the alkali silicate fireproofing sheets on both sides with a sheet of metal.

Composite sheets according to this invention may be processed direct into shaped articles by conventional deep drawing machines for working metals, and the operation may be carried out at elevated temperatures at which the fireproofing sheets are plastic but not yet expanded. This is the case at temperatures of 50 to 150 C., preferably of to 120 C. Sheet metal combined with a fireproofing sheet having, with reference to anhydrous alkali metal silicate, a water content of 50% by weight and a fiber content of 17% by weight, may for example be extended at a temperature of C. up to 60% of its original length without noticeable cracks appearing in the fireproofing sheet.

The side of the sheet metal which is not covered with a fireproofing sheet may be provided without difiiculty with a conventional baking lacquer. It is advantageous to use lacquers which are baked at temperatures of about 100 to C., because the fireproofing sheets begin to expand at higher temperatures.

Composite sheets according to this invention not only have excellent heat insulating and fiame insulating properties but also have a greatly diminished drumming effect and this makes them particularly suitable for example for vehicle construction, for example for the manufacture of body parts in motor vehicle construction.

The invention is further illustrated by the following example.

Example A fireproofing sheet 40 x 40 cm. in size and 1.2 mm. in thickness, which contains 17% of glass staple silk 5 cm. in length and 50% of Water, both with reference to anhydrous alkali metal silicate, is laid on a piece of sheet iron of the same size and a thickness of 0.4 mm. and the composite sheet is pressed for five minutes at a pressure of 100 atmospheres and a temperature of 90 C. in a laboratory press and cooled under pressure.

The composite sheet thus obtained is heated to 90 C. and shaped on a conventional deep drawing press to a ball segment having an upper diameter of 7.5 cm. and a height of 2.0 cm. A commercial lacquer based on urea formaldehyde and alkyd resin is spread on the metal face and baked for an hour at 100 C. The metal is not separate from the fireproofing sheet.

We claim:

1. A process for the production of a composite heat insulating sheet which comprises covering a sheet consisting essentially of an alkali metal silicate having a molar ratio of alkali metal oxide to silicon dioxide of 1:2 to 1:4, said sheet of alkali metal silicate containing water in an amount of 20 to 70% by weight and glass staple fibers in an amount of 10 to 40% by weight, said percentages being with reference to anhydrous alkali metal silicate contained in the sheet, with a metal sheet on at least one side, and pressing the resulting composite sheet at a temperature between 50 and C. into a coherent sheet composition.

2. A process according to claim 1 wherein said sheet composition is cooled under pressure.

3. A process for the production of a composite heat insulating sheet which comprises covering a sheet of metal on each side with a sheet consisting essentially of an alkali metal silicate having a molar ratio of alkali metal oxide to silicon dioxide of 1:2 to 1:4, said sheet of alkali metal silicate containing water in an amount of 20 to 70% by Weight and glass staple fibers in an amount of 10 to 40% by Weight, said percentages being with reference to anhydrous alkali metal silicate contained in the sheet, and pressing the resulting composite sheet at 7 3 a temperatuie between 50 and 150 C. into a coherent 2,266,638 sheet composition. 2,372,285 4. A process according to claim 3 wherein said sheet 2,404,904 composition is cooled under pressure. 2,434,466 7 References Cited by the Examiner 5 6159 UNITED STATES PATENTS 4 Hauser. Marc et a1.

Collins 161193 XR Marc 10684 XR Kendall et a1. 10684 EARL M. BERGERT, Primary Examiner.

MORRIS SUSSMAN, Examiner. 

1. A PROCESS FOR THE PRODUCTION OF A COMPOSITE HEAT INSULATING SHEET WHICH COMPRISES COVERING A SHEET CONSISTING ESSENTIALLY OF AN ALKALI METAL SILICATE HAVING A MOLAR RATIO OF ALKALI METAL OXIDE TO SILICON DIOXIDE OF 1:2 TO 1:4 SAID SHEET OF ALKALI METAL SILICATE CONTAINING WATER IN AN AMOUNT OF 20 TO 70% BY WEIGHT AND GLASS STAPLE FIBERS IN AN AMOUNT OF 10 TO 40% BY WEIGHT, SAID PERCENTAGES BEING WITH REFERENCE TO ANHYDROUS ALKALI METAL SILICATE CONTAINED IN THE SHEET, WITH A METAL SHEET ON AT LEAST ONE SIDE, AND PRESSING THE RESULTING COMPOSITE SHEET AT A TEMPERATURE BETWEEN 50 AND 150*C. INTO A COHERENT SHEET COMPOSITION. 